1. Field of the Invention
The present invention relates to a rim wheel for a vehicle to which a tire is attached, and a tire rim assembly. More particularly, the present invention relates to a rim wheel and a tire rim assembly which can suppress vibration transmitted to a vehicle at the same time as serving high steering stability thus contributing to improve merits in riding comfort, noise reduction inside the vehicle, and the like.
2. Background Art
In recent years, high functional performances in automobiles are on demand, particularly in the area of luxury automobiles, in which high functional performances good controllability, a high level of riding comfort and quietness are to be excellently secured.
In view of the aforementioned facts, in the so-called “leg vicinity” category including tires, rim wheels and suspensions, improvements has been achieved in technologies for active control of a suspension, rubber for prevention of vibration and the structure of tires.
As far as a rim wheel is concerned, Japanese Utility Model Applications (JP-U) Laid-Open Nos. 1-39103 and 1-90601, Japanese Patent Applications (JP-A) Laid-Open Nos. 1-115701 and 1-115702, and EP No. 0936083 disclose therein technology designed to reduce cavity resonance of a tire, which is the main cause of noise inside vehicles. According to the technology disclosed, sub-air chambers are provided inside a rim wheel, and a dimensional relationship between sub-air chambers and communicating holes is controlled, so that sub air chambers are operated as a Helmholtz resonance noise absorber.
The Helmholtz resonance noise absorber is a technique of which effect has been field-proven in acoustic rooms and the like, and is supposed to be effective for suppressing standing sound (noise).
The inventors have studied intensively the known documents described above in which the Helmholtz resonance noise absorber has been applied to a wheel, and they have discovered that, as described below, improvements achieved with this resonator have so far been inadequate, and that problems have been experienced in its practical applications.
In the first place, sufficient benefits cannot be obtained unless a total volume of sub-air chambers used for the Helmholtz resonance noise absorber is sufficiently big in size in relation to a volume of main air chambers of a tire whose level of noise it is intended to be reduced.
Embodiments of JP-U No. 1-90601, JP-A No. 1-115701, and EP No. 0936083 are structured such that sub-air chambers are formed in a disk or in a spoke. An embodiment of EP No. 0936083 is structured such that sub-air chambers are formed adjacent to a disk or a spoke. However, in practice, it is necessary to obtain a brake space and this makes it difficult to form a large air chamber in the same area.
More specifically, most types of automobile are equipped with a disk brake at front wheel portions, and a brake caliper is disposed somewhat close to an inner portion in a vehicle axis direction of a rim wheel spoke.
Further, from the viewpoint of the rigidity of a rim, there is a limit to possible reductions in a plate thickness of a spoke.
An embodiment of EP No. 0936083 is structured such that sub-air chambers are provided at a rim base portion. However, obtaining a large volume is also difficult. Although a certain degree of noise reduction can be expected, this is not sufficient to meet the level of reduction desired.
Moreover, in the case of a Helmholtz resonance noise absorber, the Helmholtz resonance frequency, which is determined by a relational expression of factors such as a volume of a sub-air chamber and a length, or a cross-sectional area, of a communicating hole, must be set precisely within a given range.
If errors on these factors occur, resonance frequencies deflect from one another, and a sufficient noise reduction cannot be obtained.
As methods for forming sub-air chambers inside a rim wheel, for example, as disclosed in EP No. 0936083, a casting method using a core or a casting method using an embedded hollow body, can be cited. However, obtaining dimensional or positional accuracy of sub-air chambers is difficult, and for example, there is a fear that noise reduction may be hampered by variations in lengths of communicating holes.
Furthermore, increases in manufacturing costs, deterioration in productivity and deterioration in a rotational balance can also be disadvantages.
On the other hand, since JP-U No. 1-39103 does not include so-called terms for correcting opening ends in the aforementioned relational expression of the resonance frequency, an appropriate setting cannot be achieved, making it impossible to obtain a sufficient degree of noise reduction.
Further, in an embodiment of JP-U No. 1-39103, a rim wheel is structured to have a double bottom, and considered to have a sufficient volume of sub-air chambers. However, since the rim wheel is formed into a configuration whose diameter is smaller than that of a bead baseline or does not have a so-called rim bottom portion, it is impossible for a tire bead to pass a rim flange, and in practice, rim assembly cannot be carried out. Consequently, the rim wheel according to this disclosure cannot be put to practical use.
Further, in JP-U No. 1-39103, requirements in respect of the number of air chambers in a circumferential direction of the rim wheel have not been sufficiently studied. With a single air chamber in an embodiment of this disclosure, improvements are hardly noticeable, and even with two air chambers, sufficient improvements cannot be demonstrated.
JP-A No. 1-115702 also discloses a configuration of a rim wheel having a double bottom. However, no description is given of the number of air chambers (a ring body is not divided in a circumferential direction). In this case, if the rim wheel is a continuous body in a circumferential direction, a problem is caused in that cavity resonance tends to rather increase.
Another embodiment of EP No. 0936083 or of JP-A No. 1-115702 discloses a method in which another hollow structural member is attached to a well portion in an inner radial direction thereof. However, in this case, there is a concern of deteriorations in rotational balance, and in addition, there are other drawbacks such as an increase in the number of manufacturing processes, an increase in weight, and concerns about the reliability of air seals.
EP No. 0936083 also discloses a method in which a hollow structural member is attached to a tire inner liner side of the well portion. Here, however, there is a concern of deteriorations in rotational balance, and in addition, problems occur as a result of an increase in the number of manufacturing processes and an increase in weight. Further, since, in the embodiments of this disclosure, a rim bottom portion is closed, it is difficult for a tire bead portion to pass a rim flange, thus making it extremely difficult to undertake the rim assembly.
In view of the aforementioned facts, an object of the present invention is to provide a rim wheel and a tire rim assembly in which tire cavity resonance can be reduced effectively, to secure improvements in quietness, which is a major requirement for automobiles, and in riding comfort, thus making the rim wheel and the tire rim assembly practical applications.